Class 10 Science Chapter 2 MCQ

Most of the plants grow best when the pH of the soil is close to 7. If the soil is too acidic or too basic (too alkaline), the plants grow badly or do not grow at all. The soil may be acidic or basic naturally. The soil pH is also affected by the use of chemical fertilizers in the fields. The pH of acidic soil can reach as low as 4 and that of the basic soil can go up to 8.3. Chemicals can be added to soil to adjust its pH and make it suitable for growing plants.

Our stomach produces hydrochloric acid (of pH about 1.4). This dilute hydrochloric acid helps in digesting our food without harming the stomach. Sometimes, excess of acid is produced in the stomach due to various reasons. The excess acid in the stomach causes indigestion which produces pain and irritation.

If a solution turns universal indicator green, then it will be a neutral solution (which is neither acidic nor basic). Thus, water will produce a green colour with universal indicator.

When equal volumes of hydrochloric acid (strong acid) and sodium hydroxide (strong base) solution of same concentration are mixed, the result is salt and water. This is a neutralisation reaction. You can easily understand by this equation: HCl + NaOH → NaCl + H2O

Firstly, Bleaching powder (CaOCl2) is used bleach clothes and removes colour from clothes. It decomposes on reaction with water and releases chlorine which acts as oxidising, bleaching and disinfecting agent. Baking soda is a natural antacid. It is used to relieve acidity in stomach and heart burn. Washing soda is used in the preparation of glass, soap and paper industries. Sodium chloride is used to produce H2 and Cl2 gases. And lastly, Aqueous sodium chloride on electrolysis yields hydrogen and chlorine.

All the options are characteristics of acids except one. They feel soapy. Hence, your answer will be option [B].

Aqua-regia is used for the dissolution of gold. It is a solution of concentrated HNO3 and concentrated HCl in the ratio of 1:3. Thus this solution is strongly acidic and is used to dissolve gold.

Here, all the statements are incorrect except one. Hence, your answer will be option [D]. Sulphuric acid (H2SO4) and nitric acid (HNO3) are also strong acids. Carbonic acid (H2CO3) and sulphurous acid (H2SO3) are also weak acids. Strong acids also have a high electrical conductivity.

Lime (CaO) is the base that reacts with a dilute acid such as HCl to form a salt called “Calcium Chloride”. It is an exothermic reaction and releases water but no carbon dioxide. Mable or limestone (CaCO3) or baking soda (NaHCO3) react with HCl to release CO2.

The hydrogen containing compounds like glucose and alcohol do not produce hydrogen ions or some other ions in solution. So, due to the absence of ions, glucose solution and alcohol solution do not conduct electricity.

When a small amount of acid such as hydrochloric acid is added to water, individual ions of the acid are dissociated. This process is known as “Ionization”. So hydrochloric acid separates into positively charged hydrogen ions and negatively charged chlorine ions. Mixing of an acid with water is also called dilution. Addition water results in the decrease in the concentration of ions, (H3O+) per unit volume.

When we eat, our stomach releases hydrochloric acid that helps in digestion. Acids always have pH less than 7.

Generally, acids are stored in containers made of glass and ceramics because they are not attacked by acids. Acids are never stored in metal containers because they gradually corrode and eat up the metal container.

Toothpastes we generally contain mild bases such as sodium fluoride or sodium bicarbonate in their composition. The base reacts with the acid formed during tooth decay and neutralises its bad effects thus, preventing tooth decay. Note: When we eat food containing sugar, then the bacteria present in our mouth break down the sugar to form acids (such as lactic acid). Thus, acid is formed in the mouth after a sugary food has been eaten. This acid lowers the pH in the mouth (making it acidic). Tooth decay starts when the pH of acid formed in the mouth falls below 5.5.

Baking powder is a mixture of baking soda NaHCO3 (sodium hydrogen carbonate) and a mild edible acid such as tartaric acid. When baking powder is mixed with water, sodium hydrogen carbonate reacts with tartaric acid and accepts hydrogen ions from it. This process releases carbon dioxide gas which is trapped in the dough when baking powder is used to make bread and cake.

When carbon dioxide gas is passed through lime water, the lime water turns milky due to the formation of a white precipitate of calcium carbonate: You can easily understand by this equation: Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O (l) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water

Water is added to concentrated acid to dilute it, then a large amount of heat is evolved at once. This heat changes some of the water to steam explosively which can splash the acid on our face or clothes and cause acid burns. Note: When a concentrated acid is added to water for preparing a dilute acid, then the heat is evolved gradually, and easily absorbed by the large amount of water

When sodium hydrogen carbonate is added to acetic acid, carbon dioxide (CO2) gas is evolved. Sodium hydrogen carbonate + Acetic acid → Sodium acetate + water + carbon dioxide You can easily understand by this equation: NaHCO3 + CH3COOH → CH3COONa + H2O + CO2

Firstly, we have to understand that a strong base cannot be used to neutralise the acid as it can corrode the skin. Wash the hand immediately with plenty of water as it helps to wash away most of the acid. Thereafter apply a paste of baking soda (NaHCO3) to neutralise the little acid if any, left over the hand. Baking soda has weak basic properties that is used to neutralise the acid.

The increasing order of acid strength is water < acetic acid < hydrochloride acid. Hydrochloride acid is a mineral acid and ionises completely in water. That’s why it is a strong acid. Acetic acid is an organic acid and ionises only partially in water. That’s why it is a weak acid. Water is almost neutral in nature. In pure water number of positive hydrogen ions is equal to the negative ions.

Here, all the statements are correct. Hence, your answer will be option [D].

The most common indicator used for testing acids and bases in the laboratory is litmus. Litmus can be used in the form of litmus solution or in the form of litmus paper. It is of two types blue litmus and red litmus.

Sodium carbonate (Na2CO3) is the salt formed by the combination of a weak acid such as carbonic acid (H2CO3) and a strong base such as sodium hydroxide (NaOH). You can easily understand by this equation: 2NaOH + H2CO3 → Na2CO3 +2H2O Note: The salt formed by the combination of weak acid and a strong base is basic in nature. Basic salts have pH more than 7.

The aqueous solution is a base as it turns red litmus solution blue. An acidic solution such as hydrochloric acid (HCl) would reverse the change. In contrast, hydrochloric acid would turn blue litmus solution to red.

Calcium chloride is a good dehydrating agent. It absorbs moisture or water content from the gas making it dry. Calcium chloride is widely used in many industries due to its ability to absorb water.